The invention relates to a filter arrangement for removing soot particles from the exhaust gases of an internal combustion engine, particularly a diesel engine, having at least one filter body made of a porous filter material and comprising filter ducts arranged in a honey-comb configuration. In the region of the inlet openings of the filter ducts, which are open toward the gas intake side, an electric resistance heating element is arranged which is associated with a plurality of inlet openings. This heating element enters into the filter ducts in the form of loops and is connected with a current supply by way of a lead-in line and a lead-out line.
Follow-up treatment systems for exhaust gas to reduce particle emission, particularly in diesel engines, are known. Such systems usually consist of filter systems that retain and collect the particles present in the exhaust gas. The soot particles retained in the filter cause an increase in the flow resistance in the exhaust system, resulting in an increase in the exhaust gas back pressure of the engine. This leads to increased fuel consumption and, in the extreme case, to engine stoppage. Thus, it is necessary to remove the soot particles which are deposited in the filter. This may be accomplished, for example, by oxidation at high temperatures.
So-called honey-comb filters made of a porous ceramic material have proved to be expedient as filter bodies for retaining soot particles. These honey-comb filters are configured of a plurality of parallel filter ducts which are closed alternately on the gas intake side and on the gas discharge side, so that the exhaust gases flow through the porous filter walls and thereby deposit the soot particles on the walls of the filter ducts.
To regenerate the filter, it is possible, for example, to increase the exhaust gas temperature so much that the ignition temperature for soot particles deposited on the walls of the filter ducts is reached and the particles incinerate. The temperatures required for this process are not reached as often as required, at least not in diesel engines for automobiles and thus regeneration is not ensured. Moreover, additional engine measures for increasing the exhaust temperature may be connected with a significant increase in fuel consumption. The use of additional energy, for example, by additional burners, to increase the exhaust gas temperature, requires high power and thus leads to an increase in the vehicle's energy consumption.
Energy efficient regeneration may be obtained, if the soot layer deposited at the filter body in the inlet region of the filter ducts is promptly ignited by a short-term energy supply. The release of energy during the combustion of soot which then follows, may lead to self-supporting soot combustion, since the released heat is greater than the dissipated heat.
To accomplish this, resistance heating elements, each provided with a lead-in line and a lead-out line, which provide heating zones for adjacent end-face regions, are arranged at the intake side of the end face of the filter body. Due to the division of the intake side of the end face of the filter body into a plurality of heating zones, it is possible to adjust the resistance heating elements required for this purpose with respect to the electrical energy required to produce the ignition temperature to the performance of the generator provided in the vehicle. The size of the heating zone charged by the respective resistance heating element is determined by the electrical resistance required by the heating element for the release of heat, with a given wire diameter and a given wire material, as well as the power of the available current supply, particularly, of the available generator in the vehicle. The division of the end face of the filter body into a corresponding number of heating zones makes it possible to heat practically all filter ducts in the region of their inlet openings despite the restricted availability of electrical power. This occurs in that the individual resistance heating elements are successively switched on and off again by way of a switching arrangement, so that, in a corresponding cycle, the soot deposits in the filter ducts of each heating zone are continuously incinerated.
The resistance heating elements are configured of at least one wire, which is curved in a meander pattern and whose loops are each plugged into an inlet opening of the filter duct.
The free ends of the meander are each connected to a lead-in line or a lead-out line which is spaced from and guided over the end face of the filter body. The advantage of this type of configuration is that due to the plurality of heating wires, which extend parallel to one another, and the lead-in line and lead-out line, respectively, extending transversely thereto in the end region a stable heating element is formed which permits, reliable positioning of the heating wires at their free ends.
However, due to vibrations and thermal expansion, it is possible for the meanders to move out of the ducts and thus dependable durability of the system is no longer ensured. Additional supports and/or cover disks such as described in DE-OS (Unexamined Published German Patent Application) 3,712,333 have the disadvantage of higher manufacturing costs.